The relative risk of the commonly used general anesthetics is not known. In particular, very little information concerning the effects of anesthetics on myocardial energy utilization exists. Knowledge of this kind would be extremely helpful in guiding the selection and use of these drugs in patients with ischemic heart disease where the availability of energy to the myocardium is limited. A myothermic study is proposed wherein principles of thermodynamics are employed to investigate the relationship of total energy expenditure to mechanical performance in the isolated heart and in papillary muscle. Specifically, the direct effects of general anesthetics on myocardial enthalpic efficiency, and on the energy associated with tension or pressure generation and with myocardial activation, will be determined. The effect of hypoxia in the presence of anesthetics will be investigated.